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Highlights: [•] Adjusting fertilization to the crop requirements reduces the N balance in a farmer's field. [•] N mineralized in spring is only utilized by the following summer-crop. [•] N application above crop requirements increases the amount of cycling N and apparent N loss. [Copyright &y& Elsevier]

Previous studies have shown that carbon (C) mineralization in saline or sodic soils is affected by various factors including organic C content, salt concentration and water content in saline soils and soil structure in sodic soils, but there is little information about which soil properties control carbon dioxide (CO) emission from saline-sodic soils. In this study, eight field-collected saline-sodic soils, varying in electrical conductivity (EC, a measure of salinity, ranging from 3 to 262 dS m) and sodium adsorption ratio (SAR, a measure of sodicity, ranging from 11 to 62), were left unamended or amended with mature wheat or vetch residues (2% w/ w). Carbon dioxide release was measured over 42 days at constant temperature and soil water content. Cumulative respiration expressed per gram SOC increased in the following order: unamended soil

Overused soil resources and the build-up of organic residues from industrial processes have resulted in increased risk of environmental contamination. Recycling of organic residues from industry by incorporation into agricultural soil, can provide valuable organic amendment as well as supply nutrients to crops. The effect of applying organic amendments to an agricultural sandy soil on the nitrogen nutrition of wheat (Triticum aestivum L.) and residual effects on the growth of a following maize crop (Zea mays, L.), were assessed under semi-controlled environmental conditions and were compared to nitrogen mineralization prediction obtained from an aerobic incubation. Six different organic residues (composted municipal solid waste, secondary pulp-mill sludge, hornmeal, poultry manure, the solid phase from pig slurry and composted pig manure) were added to a Cambic arenosol, incubated or used in pot experiments, to evaluate and try to predict the availability to crop plants of nitrogen released from these materials. Poultry manure was the most effective amendment in making nitrogen available and enhancing nitrogen uptake by wheat plants resulting in greater dry matter yield. The dried solid phase from pig slurry and hornmeal were also beneficial to wheat growth. There was a greater recovery of nitrogen (N), from organic materials studied, by a maize crop. Poultry manure was the residue that provided a greater residual effect on N supply to maize. [ABSTRACT FROM PUBLISHER]

Plant roots and microorganisms play an important role in the soil N cycle and plant N nutrition through the release of extracellular enzymes. In the present greenhouse pot experiment, wheat ( Triticum aestivum) seedlings were grown in a fluvo-aquic soil (Udifluvent) to investigate N mineralization and utilization in the rhizosphere of wheat. The soil received chemical fertilizer (N-labeled urea), chemical fertilizer plus manure (common urea + N-labeled swine manure) or no N. Plant roots were separated from the soil with a nylon cloth, and 1-mm increments of soil moving laterally away from roots were analyzed for N, microbial C, and the activities of invertase, urease and protease. Chemical fertilizer plus manure promoted wheat growth and N absorption significantly compared with chemical fertilizer. N from both chemical fertilizer and swine manure accumulated significantly in the rhizosphere soil within 5 mm of the roots. Fertilized N could thus move easily laterally towards roots and there was no indication that movement through the soil limited plant N supply. A large proportion of fertilizer N was lost from the soil during the wheat growing period, and N utilization efficiency was 24% for chemical fertilizer and 30% for swine manure. In addition, faster rates of N mineralization, larger amounts of microbial C, and increased activities of invertase, urease and protease occurred in the rhizosphere compared with other parts of the soil. There was a significant correlation between microbial C and N mineralization rate ( r = 0.968, P < 0.01) in the whole soil. Microbial C also showed significant positive correlations with activities of invertase ( r = 0.892, P < 0.01) and protease ( r = 0.933, P < 0.01). Further study showed that adding manure into soil increased microbial C and the activities of invertase and protease; adding urea stimulated urease activity in the same soil. Changes in soil enzyme activities in response to N fertilizers could be considered indicators for different fertilizer managements. [ABSTRACT FROM AUTHOR]

Abstract: Intensively cropped agricultural production systems should be managed to improve soil quality and ecological processes and ultimately strengthen system capacity for sustained biological productivity. We examined the long-term changes (>20 years) in soil quality and productivity with incorporation of ecological management principles in a set of intensively managed row crop systems of the upper Midwest, USA. Replicated experimental treatments include corn (maize)–soybean–wheat cropping systems under four different management regimes: (a) conventional tillage and fertilizer/chemical inputs (Conventional), (b) no tillage with conventional fertilizer/chemical inputs (No-till), (c) conventional tillage with ∼30% of conventional fertilizer/chemical inputs and a leguminous cover crop (Reduced Input), and (d) conventional tillage with no fertilizer/chemical input and a leguminous cover crop (Organic). Effects of these treatments on soils were compared by developing a soil quality index (SQI) from 19 selected soil health indicators. An old field community maintained in early succession provided a benchmark for comparison. Reduction in tillage or fertilizer (No-till, Reduced Input and Organic) resulted in increased SQI and improved crop production. The No-till (SQI=1.02) and Reduced Input (SQI=1.01) systems outperformed Conventional management (SQI=0.92) in nitrogen availability and use efficiency, soil stability and structure improvement, and microbial nitrogen processing. Improvements in soil quality corresponded with increased primary production and crop yield in these systems, illustrating the value of an ecologically defined SQI for assessing the long-term effects of fertility and tillage management regimes in agricultural production systems. [Copyright &y& Elsevier]

biological (3 and 6 weeks aerobic incubation) and a chemical method [successive extractions with cold 0.1 (H1-N) and 0.5M HCl (H2-N)] were applied to 21 soils to determine: a) the potentially mineralizable-N; b) the most useful soil variables for predicting soil-N availability; and c) their usefulness for predicting N uptake by a greenhouse wheat crop. At t = 3, both net N mineralized (NNM) and net N mineralization rate (NNMR) were correlated: a) positively with SOM- and CEC-related variables; and b) positively with soil δN and negatively with soil pH, suggesting that N-mineralization, dominated by nitrification, is associated with NO-N losses and soil acidification. At t = 6, all previously discussed variables were important for NNM, but not for NNMR, mainly controlled by the available-P content. The importance of H1-N increased with N-inputs and decreased with NO losses and soil-N. Relationships of H1-N and H2-N with soil CEC and texture showed the strong relations among nutrients content, biological activity and N mineralization, and the recalcitrance of clay-bounded SOM. Soil-N correlations with wheat-N in absolute amount (positive) and as percentage of soil-N (negative) showed an important available-N supply by N-rich soils, despite their slow N turnover. All best regression models for wheat-N included 1-2 main available nutrients. The percentage of soil-N exported to plant biomass was negatively correlated with non-crystalline Al compounds and soil δN. Mineralized-N and wheat-N pools did not share many correlations with soil properties and seemed to come from different sources; consequently, the mineralized-N, which only explained a quarter of wheat-N variance, was not more useful than soil-N for predicting it. Wheat-N and hydrolysable-N only shared a positive correlation with soil-N, highlighting that they are two mainly unrelated N pools. Nevertheless, half of wheat-N variation was explained by its negative relationship with the percentage of soil-N as (H1+H2)-N; a possible explanation is that (H1+H2)-N is biologically labile and it constitutes an important soil-N fraction only when a limiting factor for microbial N mineralization or plant growth allowed its cumulation. [ABSTRACT FROM AUTHOR]

A soil microcosm experiment was conducted to evaluate the influence of copper contamination on the dynamics and diversity of bacterial communities actively involved in wheat residue decomposition. In the presence of copper, a higher level of CO2 release was observed, which did not arise from greater wheat decomposition but from a higher level of stimulation of soil organic matter mineralization (known as the priming effect). Such functional modifications may be related to significant modifications in the diversity of active bacterial populations characterized using the DNA stable-isotope probing approach. [ABSTRACT FROM AUTHOR]

The stabilization of soil organic matter (SOM) is an important process in the context of global change and is strongly affected by soil use and management. We investigated the mineralization and stabilization of 14C-labeled wheat (Triticum aestivum L.) straw and 14C-labeled farmyard manure under different cropping systems (crop rotation, monoculture, and bare fallow) in a long-term field experiment established in 1967. Exponential decay equations were fitted to the measured data, and coefficients of the C pools and decay constants were estimated. The different organic amendment and cropping systems resulted in considerably different distributions and half-lives of three modeled SOM pool compartments. Significantly lower amounts of residual 14C-labeled material were found in the bulk soils of the bare fallow systems than the farmyard-manured crop rotation or monoculture, indicating enhanced organic matter stabilization in the latter systems. In 2004, remaining 14C-labeled amendments (as a percentage of the original application in 1967) in bulk soils were 8.7 ± 0.3% for crop rotation, 8.6 ± 0.4% for monoculture, 7.5 ± 0.7% for bare fallow farmyard-manured), and 5.0 ± 0.6% for straw-manured bare fallow. Humic acids extracted with 1 mol L-1 NaOH responded markedly to the different cropping systems regarding both their extraction yields and the remaining 14C label. In all cropping systems, the 14C in the extracted humic acids decreased rapidly with time. Remaining 14C-labeled organic residues in this fraction in 2004 (as a percentage of the original application in the fraction) were 0.315 ± 0.002% for crop rotation, 0.31 ± 0.02% for monoculture, and 0.16 ± 0.02% for bare fallow (all farmyard manured). Our study therefore shows that the investigated humic acids are a dynamic SOM pool cycling at decadal and subdecadal rates. [ABSTRACT FROM AUTHOR]

Abstract: Two-pot experiments with ryegrass and wheat plants were conducted in a Cambic Arenosol to test the reliability of N fate predicted by incubation experiments previously performed, with the same soil, to assess potentially mineralizable nitrogen from six organic wastes (municipal solid waste compost, secondary pulp mill sludge, horn meal, poultry manure, solid phase from pig slurry and composted pig manure). Two treatments, corresponding to 80 and 160kgN/ha were tested, with or without mineral N fertilization. Experimental data obtained in the pot trials was consistent with nitrogen net mineralization trend observed in the aerobic incubations with all the wastes tested. Values of potentially mineralizable nitrogen (N0) from the equations obtained by model fitting, to the incubation data, were well correlated to ryegrass and wheat N uptake. Poultry manure was the most efficient N supplier to crops. [Copyright &y& Elsevier]

Influence of long-term sodic-water (SW) irrigation with or without gypsum and organic amendments [green manure (GM), farmyard manure (FYM), and rice straw (RS)] on soil properties and nitrogen (N) mineralization kinetics was studied after 12 years of rice-wheat cropping in a sandy loam soil in northwest India. Long-term SW irrigation increased soil pH, exchangeable sodium percentage (ESP), and sodium adsorption ratio (SAR) and decreased organic carbon (OC) and total N content. On the other hand, application of gypsum and organic amendments resulted in significant improvement in all these soil properties. Mineralization of soil N ranged from 54 to 111 mg N kg-1 soil in different treatments. Irrigation with SW depressed N mineralization. In SW-irrigated plots, two flushes of N mineralization were observed; the first during 0 to 7 d and the second after 28 d. Amending SW irrigated plots with GM and FYM enhanced mineralization of soil N. Gypsum application along with SW irrigation reduced cumulative N mineralization at 56 days in RS-amended plots but increased it under GM-treated, FYM-treated, or unamended plots. Nitrogen mineralization potential (No) ranged from 62 to 543 mg N kg-1 soil. In the first-order zero-order model (FOZO), the easily decomposable fraction ranged from 5.4 to 42 mg N kg-1 soil. Compared to the first-order single compartment model, the FOZO model could better explain the variations in N mineralization in different treatments. Variations in No were influenced more by changes in pH, SAR, and ESP induced by long-term SW irrigations and amendments rather than by soil OC. [ABSTRACT FROM AUTHOR]

Mineralization of soil organic nitrogen (N) and its contribution toward crop N uptake is central to developing efficient N-management practices. Because biological incubation methods are time consuming and do not fit into the batch-analysis techniques of soil-testing laboratories, an analytical procedure that can provide an estimate of the mineralizable N would be useful as a soil-test method for predicting plant-available N in soil. In the present studies, the ability of boiling potassium chloride (KCl) to extract potentially mineralizable and plant-available N in arable soils of semi-arid India was tested against results from biological incubations and uptake of N by wheat in a pot experiment. Mineralization of organic N in soils was studied in the laboratory by conducting aerobic incubations for 112 days at 32°C and 33 KPa of moisture. Cumulative N mineralization in different soils ranged from 8.2 to 75.6 mg N kg-1 soil that constituted 2.7 to 8.8% organic N. The amount of mineral N extracted by KCl increased with increase in length of boiling from 0.5 to 2 h. Boiling for 0.5, 1, 1.5, and 2 h resulted in an increase in mineral-N extraction by 9.3, 12.7, 19.6, and 26.1%, respectively, as compared to mineral N extracted at room temperature. The boiling-KCl-hydrolyzable N (ΔNi) was directly dependent upon soil organic N content, but the presence of clay retarded hydrolysis for boiling lengths of 0.5 and 1 h. However, for boiling lengths of 1.5, and 2 h, the negative effect of clay was not apparent. The ΔNi was significantly (P=0.05) correlated to cumulative N mineralized and N-mineralization potential (N0). The relationship between N0 and ΔNi was curvilinear and was best described by a power function. Boiling length of 2 h accounted for 78% of the variability in N0. Results of the pot experiment showed that at 21- and 63-day growth stages, dry-matter yield and N uptake by wheat were significantly correlated to boiling-KCl-extractable mineral N. Thus, boiling KCl could be used to predict potentially mineralizable and plant-available N in these soils, and a boiling time of 2 h was most suitable to avoid the negatively affected estimates of boiling-KCl-hydrolyzable N in the presence of clay. The results have implications for selecting length of boiling in soils varying widely in clay content, and this may explain why, in earlier studies, longer boiling times (viz. 2 or 4 h) were better predictors of N availability as compared to 0.5 and 1 h. [ABSTRACT FROM AUTHOR]

Trifluralin is typically applied onto crop residues (trash, stubble) at the soil surface, or onto the bare soil surface after the incorporation of crop residues into the soil. The objective of this study was to quantify the effect of the type and amount of crop residues in soil on trifluralin mineralization in a Wellwood silty clay loam soil. Leaves and stubble of Potato (Solanum tuberosum) (P); Canola (Brassica napus) (C), Wheat (Triticum aestivum) (W), Oats (Avena sativa), (O), and Alfalfa (Medicago sativa) (A) were added to soil microcosms at rates of 2%, 4%, 8% and 16% of the total soil weight (25 g). The type and amount of crop residues in soil had little influence on the trifluralin first-order mineralization rate constant, which ranged from 3.57E-03 day-1 in soil with 16% A to 2.89E-02 day-1 in soil with 8% W. The cumulative trifluralin mineralization at 113 days ranged from 1.15% in soil with 16% P to 3.21% in soil with 4% C, again demonstrating that the observed differences across the treatments are not of agronomic or environmental importance. [ABSTRACT FROM AUTHOR]

The components that define cereal-grain yield potential have not been well defined. The objective of this study was to collect many differing biological measurements from a long-term winter wheat ( Triticum aestivum L.) study in an attempt to better define yield potential. Four treatments were sampled that annually received 0, 45, 90, and 135 kg N ha -1 at fixed rates of phosphorus (P) (30 kg ha -1 ) and potassium (K) (37 kg ha -1 ). Mid-season measurements of leaf color, chlorophyll, normalized difference vegetative index (NDVI), plant height, canopy temperature, tiller density, plant density, soil moisture, soil NH 4 -N, NO 3 -N, organic carbon (C), total nitrogen (N), pH, and N mineralization potential were collected. In addition, soil texture and bulk density were determined to characterize each plot. Correlations and multiple linear-regression analyses were used to determine those variables that can predict final winter wheat grain yield. Both the correlation and regression analyses suggested mid-season NDVI, chlorophyll content, plant height, and total N uptake to be good predictors of final winter wheat grain yield. [ABSTRACT FROM AUTHOR]

The silica accumulation in orchard grass (Dactylis glomerata L.) and wheat (Triticum aestivum L.) has been studied in plant samples grown under defined conditions in a pot trial. The plant habit and the quantity of biomineralised silica within the selected Gramineae depend to a remarkable extent on the soil. The plants grew with different soil pH values and silica additives. By means of atomic absorption spectrometry, the silicon enrichment in different plant parts was determined. In dried plant parts the silica bodies can be well distinguished by variable pressure scanning electron microscopy in the back scattering mode. They are located in silica cells below the epidermis and in epidermal appendices (bristles, prickle hairs). The silica bodies showed a defined morphology, structure and composition which was elucidated by the combined performance of scanning electron microscopy in combination with X-ray spectroscopy, solid-state nuclear resonance, X-ray diffraction and Raman spectroscopy. The composition was near to stoichiometric SiO2 (41 weight% silicon, 56 weight % oxygen), and the SiO4/2 tetrahedra were arranged preferentially in three-dimensional networks; a smaller proportion was in chains and layers. The silica bodies with an overall amorphous structure contained crystalline precipitates, which could be indexed by α-quartz. [ABSTRACT FROM AUTHOR]

N mineralisation and immobilisation were quantified in field conditions in the presence or in the absence of wheat residues. The incubation study was conducted in cylinders placed in microplots (no plants were grown in cylinders), and the rest of each microplot was sowed with the wheat crop (Triticum durum var. Massa). N mineralisation and immobilisation depend on the presence or the absence of wheat residues. In absence of residues, a linear model of regression was developed to follow the clear nitrogen mineralisation at different soil levels. Nitrogen mineralisation (mg kg–1), during the five months of wheat development, showed the following decreasing order: 0–15 cm (132.6) > 15–30 cm (120.6) > 30–45 cm (91.3). The mineralisation rate was 24.1, 22.9 and 18.9 mg kg–1 d–1 for 0–15, 15–30 and 30–45 cm levels, respectively. The supply of wheat residues resulted in a five months N immobilisation process. At level 0–15 cm the immobilisation (mg kg–1) showed the following decreasing order: (61.6) > (46.4) > (30.0) for the supply of wheat residues at seeding time, and 15 and 30 d before seeding respectively. At the other levels, the same decreasing order was recorded. The supply of 8 t ha–1 of wheat residues at seeding time, and 15 or 30 d before seeding, decreased the dry matter yield and N accumulation in wheat crop. In consequence, there was no synchronism between the nitrogen liberated by wheat residues decomposition and the wheat growth. [Copyright &y& Elsevier]